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Research Papers: Gas Turbines: Structures and Dynamics

Labyrinth Seal Leakage Degradation Due to Various Types of Wear

[+] Author and Article Information
Yahya Dogu

Mechanical Engineering Department,
Kirikkale University,
Yahsihan, Kirikkale 71450, Turkey
e-mail: yahya.dogu@hotmail.com

Mustafa C. Sertçakan

TUSAS Engine Industries, Inc. (TEI),
Eskisehir 26003, Turkey
e-mail: mustafacem.sertcakan@tei.com.tr

Koray Gezer

Mechanical Engineering Department,
Kirikkale University,
Yahsihan, Kirikkale 71450, Turkey
e-mail: koraygezer90@gmail.com

Mustafa Kocagül

TUSAS Engine Industries, Inc. (TEI),
Eskisehir 26003, Turkey
e-mail: mustafa.kocagul@tei.com.tr

Ercan Arıcan

TUSAS Engine Industries, Inc. (TEI),
Eskisehir 26003, Turkey
e-mail: ercan.arican@tei.com.tr

Murat S. Ozmusul

Pro Solutions USA,
LLC 453 Kinns Road,
Clifton Park, NY 12065 
e-mail: ozmusul@prousa.us

1Corresponding author.

Contributed by the Structures and Dynamics Committee of ASME for publication in the JOURNAL OF ENGINEERING FOR GAS TURBINES AND POWER. Manuscript received August 9, 2016; final manuscript received December 15, 2016; published online February 1, 2017. Editor: David Wisler.

J. Eng. Gas Turbines Power 139(6), 062504 (Feb 01, 2017) (11 pages) Paper No: GTP-16-1400; doi: 10.1115/1.4035658 History: Received August 09, 2016; Revised December 15, 2016

This paper systematically presents a complete leakage comparison for various types of wear experienced by labyrinth seals. Labyrinth seals used in turbine engines are designed to work at a clearance during steady-state engine operations. The tooth tip rubs the stator and wears either itself or the stator surface during transient operations, depending on the material properties of the tooth and stator. Any type of wear that increases clearance or deforms the tooth tip will cause permanent and unpredictable leakage degradation. This negatively affects the engine's overall efficiency, durability, and life. The teeth have been reported to wear into a mushroom profile or into a rounded profile. A rub-groove on the opposing surface may form in several shapes. Based on a literature survey, five rub-groove shapes are considered in this work. They are rectangle, trapezoid (isosceles and acute), triangle, and ellipse. In this work, leakage degradation due to wear is numerically quantified for both mushroomed and rounded tooth wear profiles. It also includes analyses on rounded teeth with the formation of five rub-groove shapes. All parameters are analyzed at various operating conditions (clearance, pressure ratio, number of teeth, and rotor speed). Computational fluid dynamics (CFD) analyses are carried out by employing compressible turbulent flow in a 2D axisymmetrical coordinate system. CFD analyses show that the following tooth-wear conditions affect leakage from least to greatest: unworn, rounded, and mushroomed. These are for an unworn flat stator. It is also observed that rub-groove shapes considerably affect the leakage depending on the clearance. Leakage increases with the following groove profiles: triangular, rectangular, acute trapezoidal, isosceles trapezoidal, and elliptical. The results show that any type of labyrinth seal wear has significant effects on leakage. Therefore, leakage degradation due to wear should be considered during the engine design phase.

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Figures

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Fig. 1

Photographs for shapes of tooth tip wear and rub-groove: (a) [4], (b) [5], (c) [6], (d) [7], (e) [8], (f) [9], (g) [10], (h) [11], (i) [4], (j) [12], (k) [7], and (l) [13]

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Fig. 2

Wear shapes for tooth and rub-groove

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Fig. 3

Representative labyrinth seal geometry and boundary conditions

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Fig. 4

Representative mesh generation

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Fig. 5

Test and CFD model comparisons: (a) straight labyrinth seal without rub-groove and (b) stepped labyrinth seal with rub-groove

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Fig. 6

Flow pattern plots for various tooth wear shapes for baseline case parameters (cr* = 1, Π = 1.5, nt = 4, n = 0 rpm): (a) nondimensional pressure contours, (b) Mach number contours, (c) velocity vectors, and (d) velocity vectors around first tooth

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Fig. 7

Static pressure change at midline of clearance for baseline case parameters (cr* = 1, Π = 1.5, nt = 4, and n = 0 rpm)

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Fig. 8

Nondimensional axial velocity at first tooth clearance region showing vena contracta effect for all four configurations for baseline case parameters (cr* = 1, Π = 1.5, nt = 4, and n = 0 rpm): (a) n = 0 krpm, (b) n = 40 krpm, and (c) n = 80 krpm

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Fig. 9

Leakage and discharge coefficient versus tooth wear shapes

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Fig. 10

Leakage and discharge coefficient for various tooth wear shapes versus: (a) pressure ratio, (b) number of teeth, and (c) rotor speed

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Fig. 11

Flow patterns for various groove shapes: (a) nondimensional pressure contours, (b) Mach number contours, (c) velocity vectors, and (d) stream function

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Fig. 12

Leakage and discharge coefficient versus groove wear shape

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Fig. 13

Normalized leakage and discharge coefficient versus normalized absolute clearance resulted from groove wear shape

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